1. Field of the Invention
The present invention relates to an image forming apparatus for a copying machine, a printer, etc, which is provided with an electrifying member disposed opposite to the surface of a photosensitive body and electrifying the surface thereof by applying electric charge thereto.
2. Description of the Prior Art
For example, in an image forming apparatus of electronic photography system, an electrifier of corona discharge system has been generally employed. However, the corona discharge system generates a great deal of harmful products such as ozone, etc. Therefore, there is caused such a problem that may result in large sizing, an increase of production cost, etc., in order to make countermeasures against them. For this reason, an ozone-free electric charge application system which hardly has such problems has recently been taken into consideration.
FIG. 4 is a view showing the outline configuration of one of the examples of such a conventional image forming apparatus A.
As shown in FIG. 4, in the conventional image forming apparatus A, an electrifying roller 12 is brought into contact with a drum-like photosensitive body 2 with pressure, and is driven in line with revolutions of the photosensitive body 2. The electrifying roller 1a is a conductive member made of, for example, silicon and nylon, and has a fixed resistance (10.sup.5 to 10.sup.9 ohms). Voltage is applied to the electrifying roller 1a through the rotation axis thereof from a power source 3.
A certain potential is applied to the photosensitive body 2 from the pressure-contacting surface of the electrifying roller 1a by application of the voltage. However, as no electric discharge is generated at this time, harmful products such as ozone, etc., are hardly generated. Namely, it is possible to achieve an ozone-free electric charge.
Next, light exposure 4 is applied to the uniformly electrified surface of the photosensitive body 2 by a light exposing means (not illustrated). An electrostatic latent image of the target image information is gradually formed on the circumferential surface of the photosensitive body 2 by this light exposure 4. And the latent image is developed by a developing roller 5 as a toner image. Next, the latent image is gradually transferred onto a sheet of paper, which is fed by a paper feeding mechanism (not illustrated), by a transferring roller 6. The sheet of paper is separated from the photosensitive body 2 after the latent image is transferred thereto and is fed to a fixing device (not illustrated), wherein the transferred toner image is fixed on the sheet of paper. The toner residues and foreign adhered substances on the photosensitive body 2, the latent image of which has been transferred, are removed by a cleaning member 7, thereby causing the photosensitive body 2 to be repeatedly used. Thus, a series of image formations are carried out.
With the conventional image forming apparatus A described above, as the electrifying roller 1a is pressure-contacted to the photosensitive body 2, there are several problems such as staining of the electrifying roller 1a, wearing thereof, staining of the photosensitive body 2 due to the roller. For this reason, it was considered (in Japanese patent publication No. Hei-3-2400765) that the electrifying roller 1a is disposed apart from the photosensitive body 2. According to the same patent publication, the clearance between the electrifying roller 1a and the photosensitive body 2 is disclosed to be 5 .mu.m to 300 .mu.m. And it is also said in the same patent publication that where the clearance is more than 350 .mu.m, insulation breakdown resulting therefrom causes a leak discharge to be generated, and the apparatus A would not be able to be used. Actually however, it is very difficult to secure the dimensional control within 300 .mu.m. For example, there is a possibility for the electrifying roller 1a to be brought into contact with the photosensitive body 2 due to a bending of the roller and the dimensional tolerance thereof. Furthermore, where the clearance is within 300 .mu.m, residues and foreign substances on the photosensitive body 2 may be brought into contact with the roller, unless they are removed by a cleaning member 7.